WINSTON-SALEM, N.C., Feb 11 (Reuters) - A major winter storm that has caused at least six deaths unfurled across much of the U.S. South on Tuesday, and forecasters warned that ice could cripple road travel and bring widespread power outages in coming days.

The storm could be "a catastrophic event" of "historical proportions," the National Weather Service office in Peachtree City, Georgia, said of the latest blast of wintry weather to hit the region.

Conditions were expected to worsen overnight, with up to an inch (2.5 cm) of ice predicted in parts of Georgia and central South Carolina.

Two to 6 inches (5 to 15 cm) of snow fell in north Georgia on Tuesday, with another 5 to 9 inches (13 to 23 cm) expected by Thursday morning, said National Weather Service meteorologist Dan Darbe.

But Darbe said ice was the bigger worry, with a quarter to three-quarters of an inch (0.6 to 2 cm) expected in the area that includes metropolitan Atlanta.

The last significant ice storm in that region was in January 2000, when up to half inch (1.3 cm) of ice left more than 350,000 people without power, Darbe said.

"We're talking a much larger area and a much larger amount of ice" in this storm, he said.

President Barack Obama signed an emergency declaration for Georgia. Governors Alabama, North Carolina, South Carolina and Mississippi declared weather emergencies and Georgia Governor Nathan Deal signed an executive order to close state government Wednesday.

The storm caused two weather-related traffic deaths in Mississippi, and three in northern Texas, authorities said. A Dallas firefighter responding to an accident on an icy road also died when a skidding car hit a parked vehicle and he fell off a highway bridge.

Officials were quick to make plans for dealing with the weather after being criticized for inadequate preparation before a storm two weeks ago. That storm paralyzed Atlanta area roads and forced more than 11,000 students in Alabama to spend the night at their schools.

SCHOOLS, OFFICES CLOSED

On Tuesday, hundreds of schools and offices were closed from Texas to North Carolina, and more closures were planned for Wednesday.

"This is not the storm we had two weeks ago, where we were playing in the snow and building snowmen. This is an ice storm," South Carolina Governor Nikki Haley said.

Central South Carolina is expected to get up to 1.5 inches (3.8 cm) of ice over the next 48 hours. The National Guard was put on alert and shelters prepared in the state.

State transportation workers in North Carolina sprayed nearly 2 million gallons (7.6 million liters) of salt brine on roads ahead of the storm, the governor's office said.

Pamela Maze, a 52-year-old teacher's assistant in Atlanta, made a grocery store run on Tuesday morning but said she was not worried about the possibility of an ice storm.

"When I'm at home, I'm at home and I don't have to come back out," she said. "I think everyone should take their time and be safe, be careful."

Up to 5 inches of snow fell in north Alabama early on Tuesday, according to the National Weather Service. State transportation officials said the snow was heavier than expected in some areas and numerous roads were closed.

In Mississippi, Ripley resident Quess Hood said his family was staying indoors after getting about 2 inches (5 cm) of snow Monday night.

"I tried to move through the driveway a little while ago and wasn't real successful," he said.

Hundreds of schools and businesses in North and Central Texas were closed or had delayed openings on Tuesday. They included more than 200 in the Dallas-Fort Worth area alone because of icy conditions overnight.

Amtrak, the U.S. passenger rail service, canceled trains in the Southeast and Middle Atlantic states.

About 1,300 U.S. flights were canceled and another 3,300 delayed on Tuesday, according to flight-tracking website FlightAware.com. (Additional reporting by David Beasley in Atlanta; Karen Brooks and Jon Herskovitz in Austin, Texas; Verna Gates in Birmingham, Alabama; Emily Le Coz in Jackson, Mississippi; Harriet McLeod in Charleston, South Carolina; editing by Gunna Dickson)